Light–matter interaction at the nano- and molecular scale Free

Light–matter interaction is an old yet continuously fascinating topic. It is of direct relevance to applications as diverse as solar energy conversion, light-emitting devices, biomedical imaging, and quantum information processing. Recent advances in materials and chemistry have allowed exquisite control over this interaction at the nano- and molecular level, and newly developed spectroscopic tools are being applied to elucidate the interaction mechanisms with unprecedentedly high temporal and spatial precision. This Special Issue collects the latest cutting-edge research under this broad context, contributed by both experimentalists and theoreticians, with a special focus on those from Asia.

Novel spectroscopic tools have been the major force behind the advancements of our understanding for light–matter interaction phenomena and mechanisms, and, therefore, an important theme of the papers in this Special Issue concerns the development and application of spectroscopy-related tools in both experiments and theory. Chen and co-workers developed high-resolution, high-sensitivity femtosecond fluorescence non-collinear optical parametric amplification spectroscopy and applied it to study excited-state vibrational cooling dynamics of chlorophyll-a.¹ Liu and co-workers developed femtosecond stimulated Raman spectroscopy and investigated ultrafast intermediate states during singlet fission in lycopene H-aggregates.² Katayama and co-workers employed the pattern-illumination time-resolved phase microscopy method to unravel the spatial charge carrier behavior in photocatalytic systems.³ Katoh and Seki studied the photoluminescence decay dynamics of anatase TiO₂ photocatalysts at the pico- and nanosecond timescales using a combination of streak camera and photon counting techniques and uncovered key insights into self-trapped excitons (STEs) in TiO₂.⁴ Time-resolved photoemission electron microscopy (PEEM) is a powerful tool to study ultrafast electron dynamics with nanometer resolution; Loh and co-workers reported the data pre-processing procedure and an algorithm to perform pixel-by-pixel lifetime mapping in PEEM.⁵ While Raman spectroscopy is a routine technique in modern studies, Rambadey et al. provided new insights into evolution of Raman line shape with probing laser power by considering the light-induced perturbation in electron–phonon coupling.⁶ Palacino-González and co-workers showed by theory that it is possible to control the nonadiabatic dynamics of charge-transfer processes by using chirped pulses in a double-pump time-resolved fluorescence spectroscopy scheme.⁷ Lan and co-workers combined on-the-fly trajectory surface hopping simulations and the doorway–window representation of nonlinear optical response functions to simulate time- and frequency-resolved fluorescence spectra and anisotropies of realistic polyatomic systems.⁸ 

Light-induced charge transfer and energy transfer lie at the center of numerous energy transduction and storage systems in nature and in artificial systems, which is also a major topic covered in this collection. Xia and co-workers studied symmetry-breaking charge separation (SB-CS) in a null-excitonic three-dimensional rigid nonconjugated trimer, providing profound insights into the role of null-exciton coupling in dominating ultrafast SB-CS in multichromophoric systems.⁹ Yang and co-workers studied the bridge effect on charge transfer and energy transfer in fullerene–chromophore dyads and found that the bond order of the bridge controls the deactivation pathways to be either electron or energy transfer.¹⁰ Cui et al. investigated the spatiotemporal evolution of ultrafast photocarrier dynamics across WS₂–ReS₂ lateral interface, which can potentially benefit the development of 2D interfacial physics and 2D lateral optoelectronic devices.¹¹ Thomas and co-workers developed a Förster resonance energy transfer (FRET) pair comprising glutathione-capped InP/GaP/ZnS quantum dots (QDs) and the fluorescent protein mCherry and studied single- and two-photon-induced FRET in these bioconjugates.¹² Sarangi and co-workers systematically investigated the interplay between photoinduced charge and energy transfer from manganese(II) doped perovskite quantum dots to p-benzoquinone.¹³ Zhao and co-workers employed a non-Markovian stochastic Schrödinger equation in momentum space, together with ab initio calculations, to study phonon-mediated ultrafast energy- and momentum-resolved hole dynamics in monolayer black phosphorus.¹⁴ Dutta and Bagchi revealed the memory effects in the efficiency control of energy transfer under incoherent light excitation in noisy environments by using Kubo’s quantum stochastic Liouville equation.¹⁵ 

Organic molecules and their assemblies (or aggregates) have been the major model systems for studying light–matter interaction. The relevant papers collected herein encompass various aspects of excited-state dynamics of molecular systems. Kobayashi et al. studied relaxation dynamics of higher excited states of perylene-substituted perylene bisimide derivatives, with important implications for exploring photocatalytic reactions involving higher excited states.¹⁶ Chen and co-workers investigated the ultrafast spectroscopy of DNA molecules after proflavine intercalation and observed ultrafast charge transfer phenomena.¹⁷ Zhang and co-workers studied the ultrafast intramolecular rotation behavior of an aggregation-induced-emission molecule in solutions with different viscosities using femtosecond transient absorption, providing a detailed photophysical picture of nonradiative processes.¹⁸ Zimmerman and co-workers studied the effect of molecular permanent dipole moment (PDM) on guest aggregation and exciton quenching in phosphorescent organic light emitting diodes, providing insights for optimizing phosphorescent OLED materials.¹⁹ Ma and co-workers applied an exciton–phonon model to simulate the distal charge separation process in an aggregated perylenediimide trimer.²⁰ Sarma and co-workers combined electronic structure theory calculations and surface hopping simulation to analyze the photochromism of a fulgide molecule.²¹ Pal and Datta applied quantum mechanical calculations to screen heavy-atom-free singlet oxygen photosensitizers for photodynamic therapy.²² Geng and co-workers conducted density functional theory (DFT)/time-dependent density functional theory (TD-DFT) calculations on a series of organic room-temperature phosphorescence (ORTP) materials and found that intermolecular donor–acceptor stacking can suppress triplet exciton diffusion for long-persistent ORTP.²³ Melinger and co-workers investigated the dissipation of heat and quantum information from DNA-scaffolded chromophore networks.²⁴ 

QDs are also ideal systems to study light–matter interaction at the nanoscale, with far-reaching implications ranging from energy conversion and light-emitting devices to quantum information processing. Feng and co-workers observed light-induced photoluminescence (PL) enhancement in chiral CdSe QD films and attributed it to photoinduced surface passivation with the assistance of water molecules.²⁵ Wang and co-workers synthesized chiral perovskite-CdSe/ZnS QD composites with high circularly polarized luminescence performance achieved through additive-solvent engineering.²⁶ Single-particle PL studies are essential for understanding the photophysics of QDs by eliminating the impact of inhomogeneous size/morphology distributions. Zhang and co-workers studied size-dependent PL blinking mechanisms of single CsPbI₃ QDs and discovered a superlinear volume scaling of biexciton Auger recombination lifetime in weakly confined QDs.²⁷ Roy and Pandey studied single-particle PL of engineered ZnS/CdSe/CdS QDs and found improved single photon emission statistics from these QDs beneficial for high fidelity single photon sources.²⁸ Datta and co-workers studied single-particle PL of immobilized FAPbBr₃ QDs and elucidated the involvement of different processes in their PL intermittency.²⁹ Other interesting mechanisms and related nanomaterials are also included in this collection. Fomichev and Burdov theoretically examined the process of direct biexciton generation in Si QDs excited by a single photon.³⁰ Scherlis and co-workers modeled the electroluminescence of atomic wires from quantum dynamics simulations.³¹ Chen and co-workers reported dynamic modulation of multicolor upconversion luminescence of Er³⁺ via excitation pulse width in lanthanide-doped upconversion nanoparticles.³² 

Metal halide perovskites and their derivatives have emerged as a novel platform for studying interesting light–matter interaction phenomena. Chen and co-workers modulated the hot carrier cooling dynamics with A-site organic cations in perovskites, suggesting the potential to use large organic cations to enable hot carrier solar cells.³³ Yuan and co-workers unraveled the rapid ion migration in perovskite solar cells by an improved circuit-switched transient photoelectric technique with nanosecond temporal resolution.³⁴ Wang et al. investigated 2D Sn-based perovskites through systematic PL studies and identified the mechanisms behind dual-peak emission and anomalous exciton decay.³⁵ Nag and co-workers studied the effect of film morphology on circular dichroism of low-dimensional chiral hybrid perovskites, providing key insights for understanding the chiroptic properties of hybrid perovskites.³⁶ Ghosh and co-workers studied the cation dependent carrier cooling and transient mobility in lead-free A₃Sb₂I₉ derivatives.³⁷ Quan and co-workers elucidated temperature and pressure-induced excitation-dependent emissions in zero-dimensional hybrid metal halides with mixed halogens.³⁸ 

Metal nanostructures supporting plasmon resonances constitute another fascinating platform for studying and engineering light–matter interaction at the nanoscale. Furube and co-workers studied the enhancement of visible light response of TiO₂ photocatalysts by 3D-deposited Ag nanowires and the underlying plasmon-induced charge separation mechanism.³⁹ Ueno and co-workers investigated coherent acoustic vibrations of Au nanoblocks and modulated the acoustic phonon frequency through Al₂O₃ layer deposition.⁴⁰ Itoh and Yamamoto mapped out the electromagnetic enhancement spectra of one-dimensional plasmonic hotspots along silver nanowire dimers on the basis of surface-enhanced fluorescence.⁴¹ Nawa and Tawa demonstrated high-spatial-resolution surface plasmon resonance imaging using a plasmonic chip, with substantially enhanced sensitivity.⁴² Plasmonic structures can be viewed as open nanocavities. This links them to an important, emerging topic in chemistry, that is, polariton chemistry dealing with chemical systems under strong light–matter coupling. Vibók and co-workers compared Lindblad and Schrödinger description pictures for simulating the coupling of polyatomic molecules to lossy nanocavities, such as plasmonic nanocavities.⁴³ Chuang and Hsu reported a microscopic theory of exciton–polariton model involving multiple molecules and found the importance of including direct intermolecular interactions in the theory.⁴⁴ Wilson and co-workers found the increase in cavity coupling strength to have a significant impact on the energies and transition dipole moments of the molecule–cavity system.⁴⁵ Xiao and co-workers theoretically examined the feasibility of manipulating photosynthetic energy transfer by vibrational strong coupling.⁴⁶ 

In addition to the topics above, this collection also includes studies of other important nanoscale systems. Mukherjee and co-workers explored the unique photophysical properties of silver nanoclusters templated by cytosine-rich customized hairpin DNA.⁴⁷ Zhou and co-workers systematically explored the photophysical properties of tin-oxo cage clusters by first-principles calculations for extreme ultraviolet photoresists.⁴⁸ Mudrich and co-workers studied fragmentation of water clusters formed in helium nanodroplets by charge transfer and Penning ionization.⁴⁹ Sun and co-workers reported the observation of a super-tetrahedral cluster of acetonitrile-solvated dodecaborate dianion via dihydrogen bonding.⁵⁰ Biswas and co-workers studied temperature-dependent dielectric relaxation of (acetamide + K/Na SCN) deep eutectic solvents.⁵¹ Emerging 2D materials are also included. Karlický and co-workers studied the excitons, optical spectra, and electronic properties of semiconducting Hf-based MXenes using first-principles calculations.⁵² Yang and Dong reported oxidation tuning of ferroic transitions in a Gd₂C monolayer system.⁵³ 

The articles contained in this Special Issue demonstrate the diversity and richness of excited-state phenomena and physical mechanisms in the broad realm of light–matter interaction at the nano- and molecular scale. The development of advanced spectroscopic tools and theoretical methods is the key enabler in the field and will continue to benefit future discoveries of exotic light–matter interaction mechanisms. Important material systems are molecules (including their assemblies and aggregates), QDs, perovskites, clusters, 2D materials, and many other low-dimensional materials. Strong coupling of these systems to nanocavities offers new exciting opportunities for reshaping their energy landscape and for directing efficient charge/energy flow at the nano- and molecular scale. We hope that the excellent works collected herein will be enjoyed by the broad chemistry and physics community, thereby stimulating even more fascinating tools, materials, and mechanisms for studying light–matter interaction at the nano- and molecular scale.

The guest editors thank the authors who contributed, the journal editors, and staff who assisted this Special Topic.